The present disclosure relates to a fringe field switching (FFS) mode liquid crystal display panel and, in particular, to an FFS mode liquid crystal display panel having a slit formed by combining two slit portions that extend in different directions.
Liquid crystal display panels have characteristics in that they have a lighter weight, a lower profile, and lower power consumption than cathode ray tubes (CRTs). Accordingly, liquid crystal display panels are used in many electronic apparatuses for a display purpose. In liquid crystal display panels, liquid crystal molecules are arranged in a predetermined direction by performing a rubbing process on an alignment film. By changing the directions of the liquid crystal molecules using an electric field, the light transmittance or reflectance is changed. Thus, an image can be displayed.
In order to apply an electric field to a liquid crystal layer of a liquid crystal display panel, a longitudinal electric field method or a transverse electric field method is used. In a liquid crystal display panel that uses a longitudinal electric field method, an electrical field in a substantially longitudinal direction is applied to the liquid crystal molecules using a pair of electrodes disposed with a liquid crystal layer therebetween. Examples of the liquid crystal display panel that uses a longitudinal electric field method include a twisted nematic (TN) mode liquid crystal display panel, a vertical alignment (VA) mode liquid crystal display panel, and a multi-domain vertical alignment (MVA) mode liquid crystal display panel. In contrast, in a liquid crystal display panel that uses a transverse electric field method, a pair of substrates are disposed with a liquid crystal layer therebetween. A pair of electrodes are disposed on the inner surface of one of the pair of substrates so as to be electrically insulated from one another. Thus, an electrical field in a substantially transverse direction is applied to the liquid crystal molecules. Examples of the liquid crystal display panel that uses a transverse electric field method include an in-plane switching (IPS) mode liquid crystal display panel in which the two electrodes do not overlap in plan view and an FFS mode liquid crystal display panel in which the two electrodes overlap in plan view.
In the FFS mode liquid crystal display panel among the various types of liquid crystal display panel, a pair of electrodes including an upper electrode and a lower electrode are disposed in different layers with an insulating film therebetween. The upper electrode includes a slit-like opening, and an electric field that passes through the slit in a substantially transverse direction is applied to the liquid crystal layer. The FFS mode liquid crystal display panel can advantageously provide a wide viewing angle and improved image contrast. Accordingly, in recent years, FFS mode liquid crystal display panels have been in widespread use.
In general, in liquid crystal display panels for color display, three sub-pixels R (red), G (green), and B (blue) are formed in a line, and a combination of the three sub-pixels form one pixel. In general, each pixel is substantially square. Accordingly, each of the sub-pixels has a vertically long rectangular shape. Therefore, in FFS mode liquid crystal display panels, since it is difficult to generate an electric field in a desired direction at both ends of the slit formed in the upper electrode, the direction in which the slit extends is made to be the longitudinal direction, as described in Japanese Unexamined Patent Application Publication Nos. 2002-014374 and 2003-322869. In this way, a decrease in the aperture ratio can be made small.
In addition, in FFS mode liquid crystal display panels, the slit extends so as to be at a slight angle with respect to the rubbing direction. Thus, the liquid crystal molecules can rotate in the same direction. For color liquid crystal display panels, a change in color caused by a change in viewing angle can be reduced by using a multi-domain technique in which the tilt angle of the slit is separated into positive and negative domains. However, since it is difficult to generate an electric field in a desired direction at either end of the slit, the number of ends of slits increases if slits that extend in different directions are provided. Therefore, the aperture ratio decreases. Accordingly, Japanese Unexamined Patent Application Publication No. 2007-264231 describes a liquid crystal display panel in which multiple domains are realized by connecting slits extending in different directions. Thus, a large aperture ratio is provided.